DESCRIPTION: This application seeks continuing support for the P.I.'s pioneering work in the use of a DC-sensitive laser interferometer in basic studies of the vibration of the cochlea partition. The three goals are a) to perform more extensive characterization of the vibration of the tectorial membrane in the apical cochlea, in which the P.I. has described for the first time a compressive nonlinearity, b) to complete an extensive series of studies of basilar membrane vibration in the basal cochlea, and c) to begin studies of vibration patterns in the cochlea middle turn. In the apical cochlea, studies will include extensive exploration of the ranges of two-tone distortion product generation, an examination of a small but potentially significant dc component to tectorial membrane vibration, and an analysis of the response phase of neural excitation, relying on neural and receptor potential recording. The overall aim is a complete description, in all turns, of the vibratory mechanics of the organ of Corti.